Hi All,

I'm trying to pass a variable length string from unmanaged code to
managed code. It's actually from a DLL written for the Pocket PC 2003
in embedded Visual C++ 4 to an app written for the Pocket PC 2003
using the .Net Compact Framework in Visual Studio .Net.

What I'm trying to do is allocate the string in the unmanaged C++ and
pass it back as an out parameter into the C#. Though I can
successfully signal the length of the string from unmanaged to
managed, the char * itself (called retrievedString in my code) remains
null on the C# side. Any hints you can give would help loads.

Here's the code:

---------------------- Managed Code ----------------------

    public unsafe class Form1 : System.Windows.Forms.Form
    {
        [snip]
        [DllImport("StringTestUnmanaged2.dll")]
        protected extern static void GetString(out int stringSize, out char
* gotString);
        [snip]
        private void getStringButton_Click(object sender, System.EventArgs
e)
        {
            int stringLength;
            char * retrievedString;
            GetString(out stringLength, out retrievedString);
            stringTextBox.Text = new string(retrievedString);
        }
    }

---------------------- Unmanaged Code .h ----------------------

char toSend[] = {'h', 'a', 'l', 'l', 'o', '\0'};
extern "C" STRINGTESTUNMANAGED2_API void GetString( int * stringSize,
char * gotString );

(where STRINGTESTUNMANAGED2_API is defined to __declspec(dllexport))

---------------------- Unmanaged Code .cpp ----------------------

STRINGTESTUNMANAGED2_API void GetString( int * stringSize, char *
gotString )
{
    gotString = (char *)malloc(STRING_SIZE);
    for (int i = 0; i < STRING_SIZE; i++)
    {
        gotString[i] = toSend[i];
    }
    *stringSize = STRING_SIZE;
    return;
}

------------------------------------------------------------------

Cheers,

Tim.

PS I've read Bart Jacobs' excellent post here
http://groups.google.com/groups?selm=1069024092.24124%40seven.kulnet.kuleuven.ac.be
http://tinyurl.com/2na6e but my code still isn't working so I wonder
if it's the unmanaged side that I've messed up.